A light-sensitive image forming material has a layer comprising a light-sensitive resin which is capable of forming an image by imagewise exposure. The light-sensitive resin is made soluble or insoluble in a solvent accompanying to its molecular structure change caused by exposure to light. The formation of an image is carried out by taking advantage of the above phenomenon of the light-sensitive resin. The light-sensitive image forming material having such light-sensitive resin is mainly utilized in the fields of photograph, printing plates and plate making, which require producing visible images. The material can be, in more detail, employed for preparation of a PS (Presensitized) lithograph and a resin relief plate, photoresists such as a film type photoresist, color proofs in prepress, and lithfilms for dot to dot work.
For example, the light-sensitive image forming material employable for giving a proof to check hue and tone of a finished print has a structure comprising a support (may be referred to as tentative support hereinafter) and a light-sensitive resin layer containing a pigment which is provided thereon or a structure comprising a support and a combination of a colorant layer containing a pigment and a light-sensitive resin layer provided thereon. If necessary, a peel layer comprising an organic polymer, or a combination of the peel layer and a barrier layer comprising an organic polymer is provided on the support.
In the case of using the above light-sensitive image forming material as the image forming material (light-sensitive transferring sheet) in the surprint method (which is one of color proofing methods), the material is imagewise exposed to light to form an image on the support or the peel layer through development and then the resultant image (i.e., separation image) is transferred to a desired support to prepare a color proofing sheet having the separation image.
Such color proofing sheet is used to check hue and tone of a finished print as mentioned above, so that a separation image formed on a light-sensitive image forming material is desired to show a distinct hue.
To form a color image on a light-sensitive image forming material, an organic pigment is employed as a colorant material in the light-sensitive resin layer, because the pigment is excellent in various characteristics such as sharpness and concentration (coloring power) and has abundant hues. The color image is obtained by applying a coating solution (which is prepared through mixing the organic pigment and a light-sensitive resin) to a support or a peel layer provided on a support to prepare a light-sensitive image forming material, and exposing imagewise the material to light and then removing a soluble portion of the resin layer by developing the exposed material in a developing solution.
In the formation of the color image, the developing solution used in the developing procedure plays a important role in the point whether a color image having excellent characteristics mentioned above can be obtained or not. As the developing solution, for example, Japanese Provisional Patent Publication Nos. 1 (1989)-282543 and 3 (1991)- 198046, U.S. Pat. No.5,004,668, No. 4,766,053, No. 4,877,712, No. 4,482,625 and No. 5,149,614 disclose an alkaline developing solution containing a specific surface active agent, which is a mixture of plural compounds having the following formula: ##STR2## and is available from Kao Atlas Co., Ltd. as a trade name of Pelex NBL.
The addition of the surface active agent to a developing solution is effective to improve wetting properties of the light-sensitive resin layer and therefore the use of such developing solution is thought to shorten the developing time.
The present inventors have studied the developing solution and discovered that use of the developing solution containing such surface active agent is not capable of forming an image having excellent characteristics (sharpness and coloring power) in a reduced developing time. In more detail, use of the developing solution is apt to bring about occurrence of fog of a coloring material on the support or the peel layer and the occurrence of fog is not satisfactorily prevented even if the developing time is lengthened.
Further, the inventors have discovered that if such developing solution is stored at a low temperature in the form of its original solution before diluting it to be frozen, the developing solution using the frozen original solution through thawing (melting) does not exhibit the excellent characteristics similar to those before the freezing, i.e., has not a satisfactory freeze-thaw stability. In more detail, when the frozen developing solution is thawed, a small amount of precipitate is observed in the solution. It is thought that this precipitation reduces the developing characteristics